In the utilization of gas sparged hydrocyclones of the type such as shown in U.S. Pat. No. 4,838,434, particularly in the deinking or other treatment of comminuted cellulosis fibrous material having print thereon by a method as disclosed in co-pending application Ser. No. 07/564,656 (now U.S. Pat. No. 5,069,751) filed Aug. 9, 1990 (the disclosure of which is hereby incorporated by reference herein), the flow rate through the hydrocyclone is controlled with an orifice, which can be adjusted by changing a pedestal component of the hydrocyclone. The orifice establishes swirl layer thickness, and therefore the flow rate of the accepts through the accepts conduit. The annular opening in which the swirl layer is formed is dependent upon the location of the tapered pedestal which is centered in a cylindrical body, and the flow across the annular opening is a function of the pressure drop across the orifice and of the radial clearance between the pedestal and the cylindrical surface.
Utilizing the gas sparged hydrocyclone as set forth above in the deinking of news print and the like, particles--such as pieces of cardboard, unrefined paper, or the like--which are oversized with respect to the annular opening become lodged between the pedestal and the cylindrical surface. As the particles build up the annular opening decreases inside and back pressure in the unit increases. The increase in back pressure decreases the efficiency of the hydrocyclone by intensifying the reject rate above desired operating conditions. The situation continues until the annular opening is finally fully obstructed. In order to unplug the unit, either before or after complete operation has ceased, it is necessary to stop the deinking process, and take the unit apart.
It has been suggested in U.S. Pat. No. 4,838,434 that if the annular gap becomes clogged that the tapered pedestal can be moved downwardly through an opening in the bottom of the hydrocyclone to thereby increase the effective gap, and allow the particles to pass through. However the implication of such a concept would require complicated sealing elements, does not allow for a larger pressure differential on the material, and may have other practical difficulties associated therewith.
According to the present invention, a hydrocyclone, and a method of deinking paper, are provided which allow practical implementation of the general concept in said U.S. Pat. No. 4,838,434 of allowing obstructing particles to pass through the annular space defined adjacent the accepts outlet of the hydrocyclone (particularly a gas sparged hydrocyclone). According to the present invention, practical implementation of this concept is provided by enlarging the diameter of the body defining the hydrocyclone below where the annular space is defined, and defining the annular space with a movable plug element that is contained--except possibly for a manual or pneumatic actuating element therefor--completely within the hydrocyclone. Preferably the plug is pressed by a spring into a position defining an annular gap with a first diameter internal opening in the body, and movable against the bias of the spring into operative association with a second diameter portion of the body, which is substantially larger than the first diameter. Such a construction not only allows the entire plug to be mounted within the hydrocyclone housing, but because of the enlarged opening past the annular gap, provides a higher pressure differential, desirable in maintaining a predetermined flow rate during normal operation, and facilitating flushing of obstructions should they collect in the annular gap.
According to one aspect of the present invention, a hydrocyclone is provided comprising: A substantially hollow body having first and second ends, and having a wall disposed about an axis and axially elongated. Inlet means for introducing a suspension into the hollow body at the first end thereof, so that the suspension flows in a vortex within the hollow body. First withdrawing means for withdrawing fluid from adjacent the axis at the first end of the body. Second withdrawing means for withdrawing suspension from adjacent the second end of the body. The hollow body having a first, relatively small, internal open diameter near the second end, and a second, relatively large, internal open diameter between the first diameter and the second withdrawing means. And, movable plug means mounted within the body near the second withdrawing means for defining an annular space controlling the flow rate through the second withdrawing means, and movable to release any substance that becomes trapped in the annular space restricting the flow through the second withdrawing means. The plug means comprising a generally cylindrical plug element biased by a spring into a position normally defining the annular space between the plug element and the body at the first diameter, and movable against the spring bias (entirely within the hydrocyclone housing) to a position wherein the plug is in association with the second diameter, at which position any substance trapped in the annular space is released to flow to the second withdrawing means. The cyclone may comprise a gas sparged hydrocyclone having a porous surface of revolution disposed within the hollow body wall generally symmetrical with the axis, and a plenum defined between the body wall and the porous surface of revolution. Means are provided for introducing fluid--typically air--into the plenum to pass through the porous surface of revolution into the vortex.
The movable plug means typically comprises means for automatically moving as a result of back pressure caused by a substance that becomes trapped in the annular space, to automatically release the substance. Fluid powered means may be provided for selectively moving the plug element against the bias of the spring by fluid pressure internal of the plug element. The fluid power means may comprise: A first internal cylindrical chamber, and a piston disposed within the first chamber and having a length less than the length of the chamber. Means for holding the piston stationary with respect to the body. And bushing means for guiding relative movement between the first chamber and the piston, so that upon application of fluid under pressure into the chamber, the plug element will move in the chamber against the bias of the spring while the piston remains stationary. Alternatively, a manual means may be provided--such as a link extending exterior of the body but connected to the plug, and surrounded by the spring--which effects movement of the plug element.
According to another aspect of the present invention, a method of acting upon a low consistency liquid-solid suspension to separate undesirable materials therefrom, utilizing a hydrocyclone having an annular space through which accepted suspension passes is provided. The method comprises the steps of: (a) Introducing the suspension into a vortex, the vortex extending in a spiral path in a first direction. (b) Sparging air into the suspension in the vortex to cause undesirable particles to attach to air bubbles and flow in a second direction, generally opposite the first direction. (c) Removing particles with air from the flow in the second direction. (d) Removing accepted suspension through the annular space adjacent an end termination of the vortex in the first direction. And, (e) should plugging of the annular space occur as a result of a substance being caught therein, which causes reduced flow of the accepted suspension, unplugging the annular space without interruption of the practice of steps (a)-(d), by increasing the size of the annular space while simultaneously exposing the substance to an enlarged volume adjacent the end termination of the vortex in the first direction, providing a high pressure differential, so that unplugging of the annular space without interruption of the practice of steps (a)-(d) occurs. The method is particularly applicable to the deinking of news print or the like, in which case step (a) is practiced by introducing the suspension of finely comminuted paper having print thereon and a consistency of about 2% or more, and step (c) is practiced by removing ink particles attached to the comminuted paper. Regardless of whether or not plugging occurs, according to the invention it is also contemplated to periodically automatically move the movable plug element defining the annular space, as by applying fluid pressure to an internal component of the plug to effect movement of the plug against spring pressure.
It is the primary object of the present invention to provide an effective hydrocyclone, such as a gas sparged hydrocyclone useful in the treatment of paper suspensions (e.g. deinking of recycled paper) to practically prevent disruption or stoppage of the hydrocyclone functionality as a result of the plugging, and without interruption of the hydrocyclone functionality. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.